The invention relates in general to security systems which allow operation upon the receipt of a properly coded signal. More particularly, the invention relates to a security system or to a barrier operator system, such as a garage door operator, employing a transmitter and a receiver which communicate via code streams having at least a portion thereof which changes with multiple operation of the device.
It is well known in the art to provide garage door operators or other barrier operators which include an electric motor connectable through a transmission to a door or other movable barrier which is to be opened and closed. Since many of these systems are associated with residences, as well as with garages, it is important that opening of the barrier be permitted only by one who is authorized to obtain entry to the area which the barrier protects. Some garage door operator systems have in the past employed mechanical lock and key arrangements associated with electrical switches mounted on the outside of the garage. While these systems enjoy a relatively high level of security, they are very inconvenient to use for a person because it necessitates them exiting their vehicle in order to send the command to open the garage door. This also may present some danger to people when the exit the relative security of their vehicle if someone may be waiting to do injury to them.
It is also well known to provide radio-controlled garage door operators which include a garage door operator unit having a radio receiver and a motor connected to be driven from the radio receiver. The radio receiver is adapted to receive radio frequency signals or other electromagnetic signals having particular signal characteristics which, when received, cause the door to be opened. More recently, such transmitter and receiver systems have become relatively more sophisticated in that they use radio transmitters which employ coded transmissions of multiple or three-valued digits, also known as xe2x80x9ctrinary bitsxe2x80x9d or other serial coded transmission techniques. Among these systems are U.S. Pat. No. 3,906,348 to Willmott, which employs a transmitter and receiver system wherein a plurality of mechanical switches may be used to set a stored authorization code.
U.S. Pat. No. 4,529,980 to Liotine et al. discloses a transmitter and receiver combination for use in a device such as a garage door operator wherein the transmitter stores an authorization code which is to be transmitted to and received by the receiver via a radio frequency link. In order to alter or update the authorization code contained within the transmitter, the receiver is equipped with a programming signal transmitter or light emitting diode which can send a digitized optical signal back to the transmitter where it is stored. Other systems also employing encoded transmissions are U.S. Pat. Nos. 4,037,201, 4,535,333, 4,638,433, 4,750,118 and 4,988,992.
While each of these devices have provided good security for the user, it is apparent that persons wishing to commit property or person-related crimes have become more sophisticated as well. It is known in the security industry today that devices are being made available that can intercept or steal rolling code.
Transequatorial Technology, Inc. sells integrated circuit code hopping encoders identified as Keeloq Model NTQ105, NTQ115, NTQ125D and NTQ129. Some of the keeloq code hopping encoders generate serial codes having fixed portions, i.e., which do not change with repeated actuation of the encoding portion of the chip and rolling code portions which alter with each actuation of the encoding portion of the chip. In order to avoid, however, having the problem of the encoding portion of the chip having been inadvertently enabled and causing the rolling code to be altered on successive enabling attempts thereby leading to a rolling code which is transmitted and not recognized by a receiver, the keeloq code hopping encoders provide a window forward system, that is they are operable with systems having code receivers which recognize as a valid code not a single rolling code, but a plurality of rolling codes within a certain code window or window of values which are the values which would be generated on a relatively small number of switch closures as compared to the total number of rolling codes available. The problem with such a system, however, might arise if a user was away for a period of time or had inadvertently caused codes to be transmitted excluding the number of codes normally allowed within the valid forward code window. In that case, the rolling code would not be recognized by the receiver and the user could not gain entry without taking other measures to defeat the locking system or the garage door operator system which might involve the intervention of a trained engineer or technician.
Texas Instruments also has a prior system identified as the Mark Star TRC1300 and TRC1315 remote control transmitter/receiver combination. The system involves the use of a rolling code encoder which increments or rolls potentially the entire code, that is it does not leave a fixed portion. The system also includes a forward windowing function which allows an authorized user to be able to cause the receiver to be enabled within a limited number of key pushes. Like the keeloq system, if the forward window is exceeded, the Texas Instruments system must be placed in a learn mode to cause the system to relearn the code. In order to place the system into the learn mode, the person must obtain direct access to the receiver to cause a programming control system associated with the receiver to be hand actuated causing the receiver to enter a learn mode. Once the receiver has learned the new code, the receiver will then construct a new valid forward code window within which valid rolling codes may be received. The problem, of course, with such a system is that if, for instance in a garage door operator, the only portal of entry to the garage door is through the overhead door controlled by the garage door operator, the user will not be able to obtain entry to the garage without possibly having to do some damage to the structure. This problem is sometimes referred to in the industry as a xe2x80x9cvaulted garage.xe2x80x9d
What is needed is an economical encoding system which provides good security by using a rolling code, but which enables a user of the system to proceed via a gradually degraded pathway in the event that the receiver detects a signal condition indicative of what might be a lack of security.
The invention relates in general to an electronic system for providing remote security for entry of actuation of a particular device. Such a system may include a transmitter and receiver set, for instance with a hand-held transmitter and a receiver associated with a vehicle such as an automobile or the like. The transmitter, upon signaling the receiver, causing the vehicle to start up or to perform other functions. The system may also be useful in a barrier operator system such as a garage door operator by allowing the garage door to be opened and closed in a relatively secure fashion while preventing persons who may be intercepting the radio frequency signals from being able to, although unauthorized, cause the vehicle to begin running or to allow access to the garage.
The system includes a transmitter generally having means for developing a fixed code and a rolling or variable code. The rolling or variable code is changed with each actuation of the transmitter. The fixed code remains the same for each actuation of the transmitter. In the present system, the transmitter includes means for producing a 32-bit frame comprising the fixed portion of the code and a second 32-bit frame comprising the variable portion of the code. The 32-bit rolling code is then mirrored to provide a 32-bit mirrored rolling code. The 32-bit mirrored rolling code then has its most significant bit xe2x80x9cdeletedxe2x80x9d by setting it to zero. The transmitter then converts the 32-bit fixed code and the mirrored variable code to a three-valued or trinary bit fixed code and a three-valued or trinary bit variable code or rolling code.
To provide further security, the fixed code and the rolling codes are shuffled so that alternating trinary bits are comprised of a fixed code bit and a rolling code bit to yield a total of 40 trinary bits. The 40 trinary bits are then packaged in a first 20-trinary bit frame and a second 20-trinary bit frame which have proceeding them a single synchronization and/or identification pulse indicating the start of the frame and whether it is the first frame or the second frame. Immediately following each of the frames, the transmitter is placed into a quieting condition to maintain the average power of the transmitter over a typical 100 millisecond interval within legal limits promulgated by the United States Federal Communications Commission. The first trinary frame and the second trinary frame are used to modulate a radio frequency carrier, in this case via amplitude modulation to produce an amplitude modulated encrypted signal. In a preferred embodiment, the radio frequency signal is amplitude modulated. The amplitude modulated signal is then launched and may be received by an AM receiver. In the preferred embodiment, the AM receiver receives the amplitude modulated signal, demodulates it to produce a pair of trinary bit encoded frames. The trinary bits in each of the frames are converted on the fly to 2-bit or half nibbles indicative of the values of the trinary bits which are ultimately used to form two 16-bit fixed code words and two 16-bit variable code words. The two 16-bit fixed code words are used as a pointer to identify the location of a previously stored rolling code value within the receiver. The two 16-bit rolling code words are concatenated by taking the 16-bit word having the more significant bits, multiplying it by 310 and then adding it to the second of the words to produce a 32-bit encrypted rolling code. In order to make certain that if the transmitter was inadvertently actuated a number of times, the authorized user can still start his car or gain entry to his garage. The 32-bit encrypted code is then compared via a binary subtraction with the stored rolling code. If the 32-bit code is within a window or fixed count, in the present embodiment 1000, the microprocessor produces an authorization signal which is then responded to by other portions of the circuit to cause the garage door to open or close as commanded. In the event that the code is greater than the stored rolling code, plus 1000, indicative of a relatively large number of incrementations, the user is not locked out of the garage, but is allowed to provide further signals or indicia to the receiver that he is an authorized user without any significant degradation of the security. This is done by the receiver entering an alternate mode requiring two or more successive valid codes to be received, rather than just one. If the two or more successive valid codes are received, the garage door will open. However, in order to prevent a person who has previously or recently recorded a recent valid code from being able to obtain access to the garage, a trailing window, in this case starting at a count of 300 less than the present stored count and including all code values between the present stored count and 300 less is compared to the received code. If the received code is within this backward window, the response of the system simply is to take no further action, nor to provide authorization during that code cycle on the assumption that the code has been purloined.
Thus, the present system provides important advantages over the previous garage door operator systems and even previous rolling code systems. The system provides a multiple segmented windowed system which provides a valid code window, a second relatively insecure code window in which two successive valid codes must be received and finally a window in which no valid codes are recognized due to the likelihood of the receiver having been stolen.
It is a principal object of the present invention to provide a security system involving a radio frequency transmitter and receiver wherein multiple security conditions may exist requiring different levels of signal security.
It is another object of the present invention to provide a secure radio transmitter receiver system which may rapidly and easily decode a relatively large code combination.